Minecraft 1.9.3 Pre-Release 2 introduced a blacklisting mechanism which allowed Mojang to block servers that violate the Minecraft End User License Agreement
This mechanism seems to be missing in Minecraft 1.9.3 Pre-Release 3
The Minecraft 1.9.3 Pre-Release 2 client would compare the sha1 of the current hostname, and the current hostname without subdomains to a list containing blocked servers.
This repository is being updated every five minutes, and it attempts to utilize the dictionary in support/dictionary to determine which server(s) have been blocked by Mojang.